How to edit vertical Video in VSE?
Indirect Method

I named the scene as Video_1_comp

Go to VSE (Video Sequence Editor) and add movie



Select Only Video Strip in VSE and Strip Menu > Set Render Size



Go to the End of the Video Clip hover cursor on Timeline and press E to set End Frame



Result of all above steps
Resolution, Frame Range, Frame Rate are set to the Source Video's settings



NOW DELETE THE VIDEO and AUDIO tracks

Go to Compositing Screen
Add > Input > MovieClip 

Add Rotate node and input Value -90 it could be 90 for some videos
Don't use Back Drop preview it is not correct even though output render is correct



Then create a new scene with Copy Settings i named it as Edit



Then go to Video Sequence editor Screen

Add > Scene... > choose the Scene in my case Video_1_comp

Set Render Resolution resolution to vertical frame Height Y:1280 px Width X:720 px

Go to 3D view Properties if its not showing already press n

Scroll down to find OpenGL Preview and un-check it

Now add the Same Movie clip source again on top of existing strip

But this time Mute/delete the Video strip and keep the audio




  Now you can edit it like any movie clip you would have edited